Modern motor vehicles are equipped with numerous sensors that provide detailed information regarding the operation of the vehicle. This information may be displayed for a driver or it may be processed and provided to various vehicle control systems. For example, an analog position sensor can provide both position information and outputs that can be used to drive an electric motor or other electromechanical devices. Many of these devices may be driven by sinusoidal excitations that vary as a function of position.
Consequently, an analog position sensor having an output that varies sinusoidally with position could be used to generate absolute angular positions as may be used in an electrical power steering system to measure the angle of rotation of the steering wheel, and/or generate reference signals to produce the desired sinusoidal phase drive currents and voltages to, for example, drive an electric motor. Applications may further include throttle position sensors, pedal position sensors in drive-by-wire systems, body height position sensors for automotive suspension systems, 3-phase sine generators for brushless motors, sine/cosine resolvers for servo motors, etc.
Although resistive-film sensors are commonly used, such sensors, however, would undesirably require a sliding contact. The use of Hall devices and magnetoresistors (MRs) sensors as contactless position sensors is well known in the art.
The operational principle of an angle encoder sensor is based upon the property of some sensing elements, collectively referred to herein as “sensing elements” or “magneto-sensing elements” to sense a component of the magnetic field passing through them. Example of such sensing elements may be Hall plates and semiconductor magnetoresistors, which sense essentially the normal component of the magnetic field passing through them. Other sensing elements, such as anisotropic magnetoresistors (AMRs), may sense essentially a co-planar component of the magnetic field passing through them.
These sensors, unfortunately, may be sensitive to eccentric placement of various components that make up the sensor, such as eccentricity of the sensed target. Moreover, if a steel ring with slits or similar structure is placed around the magnet, then such a structure tends to create discontinuities along the periphery of the magnet, thus affecting the integrity of the sinusoidal waveform of the magnetic flux.
In some angular sensing applications, there is a need of a sensor exhibiting substantial linearity over its range of operation. Unfortunately, such a substantial linearity may often be achieved just through the use of costly and complex signal processing circuitry that consumes valuable real estate in size-constrained applications.
Thus, it would be desirable to provide a compact and inexpensive contactless angular position sensor having a sinusoidally varying output and/or exhibiting good linear characteristics suitable for multiple sensing schemes and without having to utilize complex circuitry.